1. Field of the Invention
This invention relates to a pigment to be contained in the ink used for forming an image by ink jet printing methods and to an ink containing the pigment.
2. Prior Art
Nowadays, with the increased use of personal computers, the ability to print the images produced by means of such personal computer on recording papers with an image quality approaching that of silver halide photography is desired. With ink jet printing methods a solution type ink is ejected from nozzle by driving the ink with an electric field, heat, pressure or other driving means.
In aforementioned ink jet printing system, an aqueous solution is used as ink, and, as the recording paper, a recording paper having a dye receiving layer disposed on a supporting layer is generally used.
As coloring material for aforementioned aqueous ink, for printing use and for photograph use, to be used as office automation equipment of in door use, in view of convenience and to prevent clogging and equipment maintenance or for the realization of high quality images, water soluble dyes are normally used. On the other hand, for printing out door displays such as posters, sign boards, and for printing industry use such as corrugated cardboard and others, pigments durable for maintaining figures are normally used. Hereinafter, the aqueous ink containing pigment as coloring material is called pigment ink and the aqueous ink containing pigment as coloring material is called hereinafter pigment ink.
As the pigment used in pigment ink, the organic pigments having specific molecular structure represented by phthalocyanine and the like and quinacridine and the like are, as a trend, used more frequently than the inorganic pigments, which present safety problems.
However, such organic pigments are expensive, and the number of suitable types of organic pigments useful for printing full color images is limited. The ability to obtain free color tone, depends on the particle size, however, if the refractive index of molecular group forming pigment is too large, light scattering increasingly occurs when the pigments are printed on plain paper. As the result, the saturation of the image decreases, because of the adverse influence of multiple inside reflection. Moreover, as a general matter, the organic pigments exhibit a tendency of lowering the molecular light absorption coefficient by mutual mixing. As a result, the organic pigments generally have lower tinctorial power, compared to dyes, by the same amount of the addition. When the tinctorial power and saturation become lower, then the clearness of image deteriorates.
Also, for bringing pigment ink into practical use, in view of preventing the clogging at the nozzle point, the applied particle size of the applied pigment becomes also finer to secure the long range excellent dispersion stability.
For this reason, as disclosed in U.S. Pat. No. 4,533,254, the proposal on the manufacturing device to lower the pigment particle size to a colloidal level, or as disclosed in U.S. Pat. No. 4,597,794 and U.S. Pat. No. 5,229,746, resin type disperse agent to secure high dispersion stability is presented.
However, even by applying these technologies to solve dispersion stability problems, the problems of cost and color tone still remains.
In view of aforementioned circumstance, the purpose of this invention is to provide the pigment with color tone competitive to aqueous ink containing dye, to provide a more simple manufacturing process and to propose a low cost pigment ink. Also, the purpose of this invention is to provide with a pigment ink by applying aforementioned pigment.
The pigment according to this invention is considered to attain aforementioned purpose and is mainly made up of intercalation compound and wherein at least a part of the intercalation ion in said intercalation compound is replaced by intercalation ions. That is to say, this invention utilizes the possibility of dye stable fixing by intercalation reaction based upon the ion exchange of intercalation compound and to apply it to pigment area.
That is, the present invention utilizes as a pigment an intercalation compound capable fixing and holding a dye by intercalation reaction based on ion replacement.
Here, as intercalation compound, montmorillonite ore group provided with smectic structure or hydrotalcite group ore are preferable. A part of intercalation ions are replaced by dye ions, and when possible, any remaining intercalation ions not previously ion exchanged with dye ions are preferably replaced by hydrophilic ions. Anyway, the amount of the replacement by dye ions should be, preferably, at least more than 5% of the exchange capacity possessed by the intercalation compound. When the amount of the replacement by dye ion is lower than this rate, the tinting strength becomes insufficient and the clearness of the image formed by using this pigment is decreased. However, if there may remain any unabsorbed ions, the dispersion of the pigment in water becomes tremendously deteriorated. Therefore, to obtain submicron particle size, though it depends upon dye sort, it is preferable to secure the amount of absorption lower than 50% of exchange capacity.
In case of the intercalation compound of montmorillonite group ore, the dye ions which replace at least a part of the intercalation ions are either a basic direct dye or a cation dye. So, it is preferable, that any remaining non-dye substituted hydrophobic intercalation ions be replaced at least in part by hydrogen ions.
When a basic direct dye and a cation dye are, together with ions, absorbed into monmorillonite group ore layer, it is possible to increase the light resistance. This is because, that the basic direct dye and cation dye have a nature of increasing light resistance under hydrogen atmosphere. For this reason, among the intercalation ions of monmorillonite group ores, those, which, because of stereospecificity, are not be replaced with aforementioned dye, are preferably replaced by hydrogen ions.
When the intercalation ions are replaced by absorption of other ions into aforementioned layers, then the dispersibility in water becomes controllable.
On the other hand, when the intercalation compounds are composed of hydrotalcite group ore, the hydrotalcite group ores are preferably the baking of natural clay indicated by the composition formula Mg0.7Al0.3O1.16.
When the intercalation compound is made up of hydrotalcite group ore, it is preferable that the dye ions replace at least a part of the intercalation ions and any remaining intercalation ions be replaced by hydrophilic ions, preferably such as the anion of salicylic acid, or an isomer the anion of salicylic acid or the anion of salicylic acid derivative having pKa value less than 5.0.
When an anionic dye, such as a direct dye or an acid dye is absorbed, together with hydrophilic ions such as salicylic acid anion or the anion of a salicylic acid isomer or the anion of salicylic acid derivative, into the interlayer of hydrotalcite group ore, the light resistance can be increased. Especially, when aforementioned hydrophilic ions are previously absorbed, the amount of the absorption of anion dye is tremendously increased, thereby also increasing light resistance.
Also, when the intercalation ions of hydrotalcite group ore are replaced by aforementioned anion dye and hydrophilic ions sufficiently to prevent the absorption of other ions into the intercalation, control of an appropriate level of dispersibility in water is provided.
The pigments of aforementioned composition are preferably applicable as pigment ink.
That is to say, the pigment ink according to this invention is made up mainly of intercalation compound. And, at least, a part of the intercalation ions are replaced by specific dye ion showing a reverse polarity as of regarding intercalation ions to produce a pigment to be dispersed, together with dispersant and humectant, in water. As for the pigment in said pigment ink is already aforementioned, but as to the dispersant and humectant to be applied with said pigment are as follows.
In case of the intercalation compound made up of montmorillonite group ores, it is preferable to use pyrophosphoric acid or the salt in an amount of from about 20 up to 100% by weight, based upon the weight of the dye-substituted montmorillonite intercalation compound pigment as a dispersant. When the particle of said intercalation compound is atomized, the viscosity of the pigment ink tends to increase. But in such case, when pyrophosphoric acid or the salt thereof is added as a dispersant, the viscosity is decreased by its breakup effect. When the amount of pyrophosphoric acid or the salt thereof is less then 10 percent weight, then the effect is not obtained. When the amount of them is more than 100 percent weight, then the limit of the solubility is exceeded.
When said intercalation compound is made up of hydrotalcite group ores, it is preferable that polyacrylic acid or the salt thereof is used as dispersant by the addition of 100 up to 1000 percent weight ratio. As to the intercalation compound made up of hydrotalcite, when the excessive amount of the same ions as of the dye absorption ion polarity may be added, a repulsive force caused by surface electric charge on the intercalation compound in conjugated condition may brought about to prevent the coagulation of the intercalation compound particles. For this reason, when aforementioned compound may be added as dispersant, the dispersibility of intercalation compound may be stabilized. Moreover, when the amount of addition of polyacrylic acid or the salt thereof is less than 100 percent weight, it is possible to obtain sufficient effect. On the other hand, when the amount of polyacrylic acid or acid salt added exceeds 1000 percent, the image formed by such pigment is liable to be disrupted as the result of the lowered water resistence of such formed picture image.
As humectant, it is preferable to use both of a heterocyclic ketone and either glycerine or a glycerine derivative, among which heterocyclic ketone, glycerine and glycerine derivatives have hygroscopicity. The heterocyclic ketone has a solubility on dyestuff, which is absorbed into the intercalation of the intercalation compounds. Glycerine or glycerine derivatives shows no solubility for dyestuffs. For this reason, when heterocyclic ketone only is applied as humectant, ketone absorbs dye as humectant and swells. Also, when glycerine and/or glycerine derivative only is used as humectant, then the capability of discharge deteriorates and blurring of drawn images and finally even clogging of nozzle takes place. For this reason, heterocyclic ketone and glycerine or glycerine derivatives should be applied in combination, under more appropriate index of addition required.